Practicing the "siren" exercise will teach you to connect your vocal registers without the crackling sound happening in your voice. You’re going to make the sound of a siren by sliding up using an Ee. Beginning with your lowest comfortable note slide all the way up to your highest easy note and back down again. Remember to take in plenty of air just before starting this exercise and lighten up your sound as you approach the vocal break. If you struggle with a smooth transition from your chest voice to your head voice, this is an excellent exercise for you!
Go slow and don’t rush through the siren. If you can’t quite make it, sliding up and down on one breath, just practice going up – take another breath – then continue going down.
This exercise may seem a little silly, but it’s incredibly effective.